Autonomous groups/meetings are free to decide whether or not there are any such requirements for the group/meeting, including how to obtain a group conscience for the fellowship-wide vote on the proposed changes.
“Every group has the right of self-government undertaken without outside control. Every group can manage itself exactly as it pleases . . [and] may make any decisions or adopt any format it likes.” -Tradition Four, Life with Hope 3rd edition pg 71-72
Some groups/meetings may have existing requirements about how many members must be present at a business meeting to vote on a motion in order to obtain a group conscience (sometimes called a “quorum”) but other groups/meetings may not have any such requirements at all. It is entirely up to your meeting whether or not a minimum number of members must be present at a business meeting to vote on this or any other motion.
There are no requirements from MA World Services regarding how many members must participate in a group/meeting vote in order to obtain a “valid” group conscience. MA World Services has no rules or requirements about how to obtain a group conscience, MA World Services only exists as a resource, and does not govern.